1. Field of the Invention
The present invention relates to a golf ball for which high durability is required like a golf ball used in a golf driving range, and more particularly, to a golf ball having indicia of superior durability and that the indicia or mark printed on a golf ball will not peel off or wear out, even if the golf ball is subjected to repeated hitting or cleaning.
2. Description of the Related Art
In general, a golf ball is printed with marks such as brand names. A clear paint is applied on the entire surface of the golf ball so as to cover the mark printed thereon, thereby imparting a gloss to the golf ball as well as protecting the mark.
A multi-piece golf ball generally comprises a rubber core and a cover covering the rubber core. The multi-piece golf ball usually employs an ionomer cover, which is formed mainly from an ionomer, because of its excellence in its repulsion property and durability. An urethane paint is preferably used as the clear paint because urethane paint follows the deformation of the golf ball when the golf ball is hit.
Since adhesion between the ionomer cover and the urethane clear paint coating is poor, it is a general practice to interpose a primer layer, which exhibits good adhesion to both the cover and the clear paint, between the cover and the clear paint layer. According to this practice, the desired mark is printed on the primer layer, and then the clear paint is applied on the entire surface of the cover so as to cover the printed mark. Japanese unexamined patent publication No. H08-182775, for example, has proposed a golf ball for which a polyurethane primer paint is used. The polyurethane primer paint contains a polyol and a polyisocyanate so that the ratio between the amount of the hydroxyl group of the polyol and the isocyanate group of the polyisocyanate is adjusted to fall within a specific range. When the clear topcoat forming the surface layer of the golf ball peels off, the printed mark sometimes peels off together with the clear topcoat due to the adhesion therebetween. Particularly when the adhesion between the clear topcoat and the primer coat is enhanced excessively, both the primer coat and the mark printed thereon sometimes peel off together with the clear topcoat. For this reason, it is preferable not to enhance the adhesion to an excessive extent between the clear topcoat and the primer coat. Rather, it is desired that only the clear topcoat peels off and that the printed mark remains on the golf ball as it is. The golf ball on which the printed mark remains is worth using even if the topcoat peels off at the golf practice driving range where the golf ball is repeatedly hit, cleaned and reused.
In some cases, the primer coat is used to enhance the adhesion of the printed mark to the cover rather than to enhance the adhesion to the clear topcoat. In addition, it has been proposed that the primer coat is removed for the purpose of simplifying the manufacturing process by enhancing the adhesion of the mark to the cover. For example, Japanese Patent No. 3,102,817 has proposed a golf ball bearing a mark printed with an ink directly on an ionomer cover. The ink contains a nitrocellulose resin exhibiting a high adhesion to the ionomer cover as a major component. However, the durability of the mark printed with nitrocellulose ink is still insufficient to meet the level of golf ball which requires a considerably high durability such as a golf ball which is repeatedly hit, used and cleaned at a golf driving range.
The present invention has been achieved in view of the foregoing circumstances. Accordingly, it is an object of the present invention to provide a golf ball both bearing a mark which can be printed directly on the cover including an ionomer cover as a major component without the need of a primer coat and which exhibits excellent durability, particularly in peel resistance and wear resistance, to such a degree as to satisfy the requirements of severe usage like the repeated cleaning.
According to the present invention, there is provided a golf ball comprising a core, a cover covering the core, and a mark printed on a surface of the cover, wherein: the cover is formed from a mixture of an ionomer and an epoxy group-containing polymer; and the mark is printed with an ink comprising a pigment, an isocyanate compound, and a base resin which is curable with the isocyanate compound.